1. Field of Invention
The invention relates to a semiconductor sensor and in particular to a semiconductor piezoresistive sensor and an operation method thereof.
2. Related Art
Pressure sensors have been widely used in various fields. According to different application fields and requirements, the principles of the pressure measurements include a piezoresistive type, a piezoelectric type and a capacitive type. Because the piezoresistive sensor has advantages such as high output voltage and high sensitivity, the measurement can be performed by utilizing the effect that the resistance of the material changes according to different stress.
FIG. 1A is a schematic cross-sectional view showing a conventional semiconductor piezoresistive sensor 1. Referring to FIG. 1A, the semiconductor piezoresistive sensor 1 includes a semiconductor base 10, a piezoresistive element 11 and a circuit 12. The semiconductor base 10, such as a monocrystalline silicon base, includes a diaphragm 101 and a base 102. The base 102 fixes both ends of the diaphragm 101, and the piezoresistive element 11 is disposed within the diaphragm 101 for serving as the sensing device of the semiconductor piezoresistive sensor 1. The circuit 12 is electrically connected with the piezoresistive element 11 and the circuit 12 includes, for example, a complementary metal oxide semiconductor (CMOS), a bridge circuit, an amplifier circuit or a logic circuit for receiving and processing the signal output from the piezoresistive element 11.
The semiconductor base 10 is an n-minus(n−)-type semiconductor, which is transferred into a p-minus(p−)-type piezoresistive element 11 by way of diffusion or ion implantation. Herein, a p-n junction is formed between the semiconductor base 10 and the piezoresistive element 11. As shown in FIG. 1A, both ends of the piezoresistive element 11 are electrically connected with a p-plus(p+)-type interconnect element 13, respectively. The circuit 12 is electrically connected to the p+-type interconnect element 13 through an opening 141 formed on an insulating layer 14, which covers the surface of the semiconductor base 10.
When a voltage V is inputted to the semiconductor piezoresistive sensor 1, a negative space charge is formed below the p-type piezoresistive element 11, and the negative space charge drifts with time so as to cause the resistance of the piezoresistive element 11 to change with time such that the output signal of the piezoresistive element 11 drifts with time. In addition, the insulating layer 14 binds some positive surface charges due to the material characteristic of the insulating layer 14, which also causes the positive surface charges to drift with time, the phenomenon relating to the resistance of the piezoresistive element 11 that varies with time becomes more serious. Accordingly, the precision of the output signal of the piezoresistive element 11 is deteriorated.
To solve the above-mentioned problem, another prior art discloses that an n-plus(n+)-doped region 15 is formed within the semiconductor base 10, as shown in FIG. 1B. Then, a proper voltage is inputted to the n+-doped region 15 to form a reverse bias at the p-n junction so as to limit the current in the piezoresistive element 11. Thus, the phenomenon of the reduced precision of measurement of the semiconductor piezoresistive sensor 1 due to the leakage current can be improved. However, in the process of manufacturing the conventional p−-type piezoresistive element 11, additional manufacturing processes, such as doping and thermal diffusion, and costs for masks which are necessary during the process of forming a n+-doped region 15 within the n−-type semiconductor base 10.
Therefore, it is an important subject of the invention to simplify the manufacturing process and effectively improve the phenomenon that the resistance of the piezoresistive element varies with time.